• 대한전기학회논문지:전력기술부문A
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• 제52권9호
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• pp.493-499
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• 2003

This paper presents exact Autotransformers(ATs)-fed AC electric Railroad system modeling using constant current mode for locomotives. An AC electric railroad system is rapidly changing single-phase load, and at a feeding substation, 3-phase electric power is transferred to paired directional single-phase electric power. As the train moves along a section of line between two adjacent ATs. The proposed AC electric railroad system modeling method considers the line self-impedances and mutual-impedances. The constant current mode model objectives are to calculate the catenary and rail voltages with the loop equation. When there are more than one train in the AC electric railroad system, the principle of superposition applies and the only difference between the system analyses for one train. Filially, this paper shows the general equation of an AC electric railroad system, and that equation has no relation with trains number, trains position, and feeding distance.

• Current Optics and Photonics
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• 제6권2호
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• pp.191-195
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• 2022

We investigate the lateral far-field pattern characteristics, including divergence angle change and far-field pattern analysis as output power increases, of narrow-emitter-width 850 nm GaAs/AlGaAs laser diodes (LDs). Each LD has a cavity of 1200 and 1500 ㎛ and narrow emitter width of 2.4 ㎛ for the top and 4.6 ㎛ for the bottom. The threshold currents are 35 and 40 mA, and L-I kinks appear at power levels of 326 and 403 mW, respectively. The divergence angle tends to increase due to the occurrence of first-order lateral mode and the thermal lensing effect. But with the L-I kink, the divergence angle decreases and the far-field pattern becomes asymmetric. This is due to coherent superposition between the fundamental and the first-order lateral mode. We provide detailed explanations for these observations based on high-power laser diode simulation results.

• Steel and Composite Structures
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• 제46권2호
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• pp.221-236
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• 2023

In order to study the seismic response of the main plant of steel reinforced concrete (SRC) structure of the CAP1400 nuclear power plant under the influence of different high-mode vibration, the 1/7 model structure was manufactured and its dynamic characteristics was tested. Secondly, the finite element model of SRC frame-bent structure was established, the seismic response was analyzed by mode-superposition response spectrum method. Taking the combination result of the 500 vibration modes as the standard, the error of the base reactions, inter-story drift, bending moment and shear of different modes were calculated. Then, based on the results, the influence of high-mode vibration on the seismic response of the SRC frame-bent structure of the main plant was analyzed. The results show that when the 34 vibration modes were intercepted, the mass participation coefficient of the vertical and horizontal vibration mode was above 90%, which can meet the requirements of design code. There is a large error between the seismic response calculated by the 34 and 500 vibration modes, and the error decreases as the number of modes increases. When 60 modes were selected, the error can be reduced to about 1%. The error of the maximum bottom moment of the bottom column appeared in the position of the bent column. Finally, according to the characteristics of the seismic influence coefficient αj of each mode, the mode contribution coefficient γj•Xji was defined to reflect the contribution of each mode to the seismic action.

• 대한기계학회논문집
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• 제16권4호
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• pp.737-752
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• 1992

본 연구에서는 링크를 여러개의 2절점 6자유도의 보 요소로 이상화하고 링크 의 운동을 평면 운동으로 한정하며 링크의 지지부의 강성은 무한대이고 회전 대우 부 분의 간극은 없는 것으로 가정하여 링크의 탄성 변형에 관한 운동 반정식을 유도하였 다. 즉, 변위법에 기초한 정적 변위 해석에 관한 유한 요소법에서 관성력, 중력 그 리고 외력을 외부 부하로 간주하여 동적인 운동 방정식을 유도하였다. 여기에, 회전 대우의 베어링을 선형 스프링으로 이상화하여 유연성 링크의 일부분으로 고려함으로써 베어링의 탄성 변형이 유연성 링크의 동적 변형에 미치는 영향에 대하여 고찰하였다. 베어링의 탄성 변형이 고려된 유연성 링크에 관한 운동 방정식을 모우드 중첩법에 근 거를 둔 수치해법으로 그 해를 구하였다.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2011년도 정기총회 및 추계학술대회 논문집
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• pp.3147-3155
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• 2011

Railway bridges are highly susceptible to resonance due to the equidistant axle load with constant speed of train. Thus, it is inevitable verify dynamic characteristics and quantities against dynamic guidelines. Recently, various new-type bridges are developed and applies to medium span length between 30m and 40m. However, just steel box girder bridge is under review for span length between 45m and 50m without development any new technologies. This study investigate the dynamic properties and safety of steel box railway bridge having span length 45m in alternative girder hight and kind of ballast. Numerical analysis is performed time series analysis by mode superposition using calculated natural vibration frequency and mode after carry out a free vibration analysis and extract modal parameter to higher modes. The results are then compared to various dynamic stability standards toward target bridge's dynamic stability analysis. The result of this study is expected as a reference for design railway bridges.

• 대한토목학회논문집
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• 제14권5호
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• pp.1105-1113
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• 1994

각종 구조물의 설계에 있어서 동적해석은 필수적이다. 이러한 구조물의 동적해석에 모우드 중첩법을 사용할 경우 고유치문제의 해석이 선행되어야 한다. 그러나 동적해석에 있어서 대부분의 노력, 즉 시간은 고유치와 그에 대응하는 고유벡터를 구하기 위하여 사용되기 때문에 보다 효율적인 고유치해법의 개발이 요구된다. 본 논문은 수치적 불안정성을 해소하고 수렴성을 향상시킴으로써 전체 해석시간을 줄이기 위해 Robinson-Lee 방법에 accelerated Newton-Raphson 방법을 적용한 고유치해법을 제시하였다. 제안방법의 효율성은 몇가지의 수치해석을 통해서 증명하였다.

• Journal of Advanced Marine Engineering and Technology
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• 제36권6호
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• pp.844-849
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• 2012

양방향 컨버터는 신재생에너지를 이용하는 전력시스템, 무정전 전원 공급장치, 전기차 등 여러분야에서 사용되며, 양방향 절연 컨버터는 양방향 비절연 컨버터보다 높은 신뢰성을 갖지만 효율이 낮다는 단점이 있다. 본 논문에서는 개선된 효율을 가지는 절연된 양방향 Zeta-Flyback 컨버터를 제안한다. 이 컨버터는 양방향 Flyback 컨버터와 양방향 Zeta 컨버터의 중첩으로서 순방향 동작과 역방향 동작에서 전력 흐름이 변압기와 소자를 통해 수행되어 변압기 이용률이 증가하고, 출력 전압은 스위치의 일정 주파수 PWM의 듀티비에 의해 제어된다. 제안된 양방향 Zeta-Flyback 컨버터와 양방향 Flyback 컨버터를 비교하면 제안된 양방향 Zeta-Flyback 컨버터가 더 높은 효율을 갖으며 이를 시뮬레이션과 실험을 통하여 확인하였다.

• 한국정밀공학회지
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• 제25권5호
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• pp.77-81
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• 2008

Structural components subjected to high frequency vibrations, such as those used in vibrating parts of gas turbine engines, are usually required to avoid resonance frequencies. Generally, the operating frequency is designed at more than resonance frequencies. When a vibrating structure starts or stops, the structure has to pass through a resonance frequency, which results in large stress concentration. This paper presents the transient thermoelastic stress analysis of vibrating cantilever beam using infrared thermography and finite element method (FEM). In FEM, stress concentration factor at the 2nd resonance vibration mode is calculated by the mode superposition method of ANSYS. In experiment, stress distributions are investigated with infrared thermography and dynamic stress concentration factor is estimated. Experimental result is agreed with FEM result within 10.6%. The advantage of this technique is a better immunity to contact problem and geometric limitation in stress analysis of small or micro structures.

• 한국자동차공학회논문집
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• 제21권3호
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• pp.148-156
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• 2013

Since the demand for new military vehicle to fulfill the necessary conditions such as multi-purpose, high-mobility, and survivability has raised continuously from the army, the prototype of a Korean light tactical vehicle was developed to meet these requirements using our own technology. In particular, the new tactical vehicle was equipped with a double wishbone independent suspension to improve ride and handling and maximize off-road driving performance. In this paper, a comprehensive virtual durability process to evaluate the service life of the prototype is presented. A reliability of the trimmed body model based on CATIA data was verified by comparison result between mode analysis and modal test. The dynamic model was constructed using ADAMS/Car, and then the weight distribution and lateral slope driving performance of it were compared with the results of static weight and lateral slope tests. The validity of the VTL(Virtual Test Lab) was checked with test results from the 3-inch spaced impact road. The durability performances of trimmed body and suspension components were evaluated through MSM(Modal Superposition Method) fatigue analysis. It is shown that the virtual durability process could be a helpful tool to find out the weak areas and improve their structures in developing new military vehicle.

• Structural Engineering and Mechanics
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• 제69권6호
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• pp.627-635
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• 2019

In order to study the axial compression performance of sand-lightweight concrete-filled steel tube (SLCFST) stub columns, three circular SLCFST (C-SLCFST) stub column specimens and three SLCFST square (S-SLCFST) stub column specimens were fabricated and static monotonic axial compression performance testing was carried out, using the volume ratio between river sand and ceramic sand in sand-lightweight concrete (SLC) as a varying parameter. The stress process and failure mode of the specimens were observed, stress-strain curves were obtained and analysed for the specimens, and the ultimate bearing capacity of SLCFST stub column specimens was calculated based on unified strength theory, limit equilibrium theory and superposition theory. The results show that the outer steel tubes of SLCFST stub columns buckled outward, core SLC was crushed, and the damage to the upper parts of the S-SLCFST stub columns was more serious than for C-SLCFST stub columns. Three stages can be identified in the stress-strain curves of SLCFST stub columns: an elastic stage, an elastic-plastic stage and a plastic stage. It is suggested that AIJ-1997, CECS 159:2004 or AIJ-1997, based on superposition theory, can be used to design the ultimate bearing capacity under axial compression for C-SLCFST and S-SLCFST stub columns; for varying replacement ratios of natural river sand, the calculated stress-strain curves for SLCFST stub columns under axial compression show good fitting to the test measure curves.